Not Applicable
Not Applicable
The present invention concerns a rocker arm device suitable for optimizing the functioning of internal combustion engines by controlling the opening and the timing of the cylinder valves according to the engine load and its speed.
For this purpose, it is already known how to use compound rocker arms consisting of two elements as specified in the Italian patent application No. MI97A002067 filed Sep. 11, 1997 in the name of Majo Cecur, assigned to the assignee of the present invention, and incorporated herein by reference. The first element consists of a rocking body, acting as a third-order lever, hinged at one end to an hydraulic lash adjuster, while the other end controls, by a shoe, the valve stem.
The second element comprises a lever, at one end of which is pivoted a roller, which receives the thrust of the cam of the distributing shaft (camshaft), while the opposite end of the lever terminates in an eyelet and is hinged to a pin which can turn within a pivot seat fashioned in said eyelet. The pin is torsionally linked to an eccentric support shaft, the rotation of the shaft being able to shift lengthwise the free end of the lever bearing the roller, so as to vary the position of incidence of the end of the lever itself by influencing the length of the arm of the body of the first element and, therefore, the valve lift and, in part, the timing of the latter. Such an arrangement is referred to as a VRRS (variable ratio rocker system).
With the known device, however, changes in the timing are accomplished only as a result of the particular geometrical shape selected for the cam.
The purpose of the invention is to improve the performance of the known device, enabling a subsequent and independent variation of the timing, along with a regulation of the valve lift.
In the device according to the invention, a pair of rocker arms is placed one within the other and is able to oscillate jointly or independently, and influence in a controllable manner the travel of the shoe associated with the engine poppet valve, thus controlling the valve lift.
The two rocker arms are linked together at one end by means of a common transverse pin, acting as a shoe on the head of the poppet valve, while at the other end the rocker arms are traversed by a compound pin controlled by an hydraulic or electrical actuator which can move transverse to the rocker arms, between two positions, enabling the coaxial and simultaneous oscillation of the two rocker arms in unison in one condition, or the independent oscillation of the rocker arms in the other condition.
For each rocker arm, the distributing shaft (camshaft) is provided with a cam arrangement, specifically, a central cam, acting on the inner rocker arm, which has less eccentricity than the eccentricity of a pair of identical cams, mounted at the sides of said central cam and acting on cheeks or lateral plates of the outer rocker arm to accomplish a larger valve opening and a longer advance.
The thrust of the central cam is transmitted to a needle roller, mounted at the end of an L-shaped lever, the fulcrum of which can be displaced lengthwise with respect to the axis of the rocker arms by means of an eccentric rotating pin. The pin rotates relative to the end of an auxiliary arm which, at the other end, accommodates the seat for the axis of oscillation of the pair of rocker arms.
Through the above mentioned auxiliary arm, which rests against a tappet, one can indirectly guarantee the contact of the inner rocker arm with the roller, the L-shaped lever, and the central cam of the distributing shaft, while the contact of the outer rocker arm with the two outer cams is obtained by means of an auxiliary elastic element connected between the L-shaped lever and the shoe.